Alumina may come in several forms, depending on its manufacturing process.
The melting of bauxite makes it possible to obtain alumina known as “brown corundum”. Brown corundum typically comprises an iron oxide content of the order of 0.2% to 1% for the purest products.
Alternatively, following the Bayer process, bauxite may be treated with soda, then calcined in order to carry out a purification. However, soda still remains, typically at contents of the order of 0.1% to 0.3% Na2O. The alumina obtained is conventionally known as “calcined alumina”.
Calcined alumina may be ground until a median size typically of around 0.5 to 50 microns, or even 0.3 to 10 microns, is obtained. The alumina obtained, referred to as “reactive alumina”, is conventionally used for manufacturing technical ceramics. The sintering of calcined alumina particles makes it possible to manufacture coarse or fine particles, generally having the shape of platelets. The alumina thus obtained is known as “tabular alumina”. Reactive alumina comprises, like tabular alumina and calcined alumina, a relatively large amount of soda.
Calcined alumina may also be fused in order to manufacture alumina known as “white corundum”, which also comprises a large amount of soda, typically of around 0.2% to 0.4%.
Beyond these conventional aluminas, manufacturers such as Aluchem Inc. supply very pure alumina powders, comprising less than 0.1% soda. These aluminas are typically used for catalytic applications or the manufacture of single crystals. Sintered refractory products with a high alumina content that comprise an aggregate of mullite and/or of tabular alumina bonded by an aluminous matrix are known.
This type of refractory product may in particular form all or part of the inner lining of the combustion chamber of a gas turbine. The lining then typically has between 10% and 50% by weight of mullite, 50% to 90% of alumina and less than 5% of silica. The lining is subjected to very high thermomechanical stresses and also to a significant corrosion by the combustion gases, and in particular by high-temperature steam. This results in particular in a decomposition of the mullite and an attack of the silicate-based glassy phase.
U.S. Pat. No. 3,067,050 describes a refractory material produced from a mixture of 72% to 90% of alumina and less than 10% of amorphous silica, fired at around 1500° C.
US 2009/0181257 describes a material intended for a combustion chamber of a gas turbine.
One objective of the present invention is to provide a product with a high alumina content that has an improved thermomechanical resistance, and in particular an improved flexural strength at high temperature, and a high resistance to corrosion, especially by steam and the gases present in a gas turbine.